Efficient video down conversion algorithm using modified IDCT basis functions

A traditional method for down conversion of MPEG compressed video performs low-pass filtering and sub-sampling after full decompression. However, the method has two shortcomings; large memory requirement and high computational complexity. To overcome the drawbacks, recent research has focussed on down conversion in the DCT domain. Existing DCT domain methods need only a quarter of full frame memory because completely reduced frames are stored in the frame memory. But the loss of field information often causes significant error during motion compensation. To solve this problem, we adopt a hybrid structure where field information is preserved by performing down conversion in the DCT domain only for horizontal direction and down conversion in the spatial domain for vertical direction. Furthermore, we present a novel technique for the horizontal down conversion which adopts a modified 4-IDCT kernel. The modified 4-IDCT kernel outperforms the conventional 4-IDCT kernel in that it performs low-pass filtering and sub-sampling additionally. Experimental results show that the proposed scheme provides high visual quality while maintaining comparable complexity.